The invention concerns the use of tires equipped with a safety insert and, in particular, detection of the bearing of a tire on the safety insert. It proposes an insert which warns the driver as soon as the tire is bearing on it after a flat or in case of substantial pressure loss, as well as a device for sensing the tire bearing on the insert, which can be combined with the insert proposed.
The function of these safety inserts, which are generally mounted on the rim inside the tire, is to bear the load in case of failure of the tire.
Bearing of the tire on the safety insert is accompanied by a more or less marked deterioration of its performances, which can fail to be perceptible to the driver through the behavior of the vehicle and the discomfort of the passenger. Furthermore, the operating lifetime of these inserts is limited. It is therefore essential, for the driver's safety, for the driver to be warned as soon as a tire is bearing on its safety insert, so that the driver can follow the manufacturer's instructions.
Several safety inserts incorporating means for so warning the driver have previously been proposed.
U.S. Pat. No. 4,262,724 discloses a safety insert intended to be mounted in an assembly comprising a tire and a rim and radially on the outside of the rim. This insert has a radially outer surface which defines a radial bearing for the crown of the tire, when the tire is deflated, as well as means for generating vibrating warning signals on running flat. These means can be a variation of the rolling radius under bearing of the insert between a minimum radius and a maximum radius in order to create a rolling vibration or one or more bumps. All the vibrating warning signals generated by these means are oriented in the plane of the tire and rim assembly and, more specifically, in a roughly vertical direction.
These solutions pose several problems. In addition to marked discomfort for passengers of the vehicle, they can markedly degrade the performance of the tire and rim assembly concerned, particularly on acceleration and braking. Thus, all one can do is avoid instantaneous stoppage of the vehicle in case of failure of the tire. On the other hand, when it is desired to use the vehicle, even at limited speed, over long distances, the warning transmitted by the insert has to be compatible with driving safety, not detrimental to the mechanics, while remaining perfectly noticeable to the driver either directly or through a suitable detection device.
Patent application WO 94/03338 also proposes a device for the detection of the bearing of a tire on a safety insert. This device comprises a wheel accelerometer, placed on one of the wheel suspension elements and measuring vertical accelerations. The accelerometers are connected to a central processing unit. The analysis is based on detection of the appearance of a resonance mode characteristic of the run-flat condition.